The present invention pertains to vapor barriers used to prevent vapor intrusion into insulation. Vapor barriers keep moisture from condensing inside insulation which otherwise would cause it to lose much of its insulating value.
The roof structure of an industrial building is typically comprised of parallel pulins mounted at the ends on horizontal I-beams which are supported by vertical columns. As U.S. Patent No. 4,075,807 sets forth, generally, insulation is either laid across the top of the purlins perpendicular thereto, with sheets of rigid roofing material then attached to the purlins through the insulation, or laid in between the purlins, and parallel to them, on top of an underlying support framework which is attached to the purlins. In either case, the underside of the insulation is laminated with a vapor impermeable facing to minimize vapor intrusion. Such a laminated vapor impermeable facing is, by itself, an ineffective vapor barrier, inasmuch as vapor can leak through the seams between adjacent sheets of insulation, or between the sheets of insulation and the purlins.
The present invention eliminates all such vapor leaks by providing a continuous vapor impermeable surface to underlie the insulation. Additionally, the instant invention provides a facing construction which securely supports the overlying insulation.
The instant invention is a vapor barrier facing construction which is installed on the underside of ceiling purlins, to both support overlying layers of insulation, which are installed between the purlins, and protect the insulation from vapor intrusion by providing a continuous vapor impermeable surface across the entire ceiling.
The invention utilizes a facing material which is both vapor impermeable and sufficiently strong to support the overlying insulation. The facing material is installed on adjacent purlins in rectangular sheets which are locally reinforced along the longitudinal edges by metal strips sealed in the facing material. The longitudinal sides of the sheets are attached to the purlins along their reinforced edges in an overlapping manner. The ends of the sheets are secured again along their reinforced edges to the beams supporting the purlins. Thus, a continuous vapor impermeable surface is created which is securely fastened along the edges of the ceiling, and contains no joint or seam which is vulnerable to vapor leak. Moreover, the facing construction solidly supports overlying insulation which is installed on top of it.
The present invention therefore comprises a highly effective vapor barrier which increases insulation efficiency, and hence, conserves energy.